Conventionally, as catalysts for purification of exhaust gas mounted on automobiles and the like, three-way catalysts, oxidation catalysts, NOx storage reduction-type catalysts, and the like have been developed to remove harmful components such as harmful gases (hydrocarbons (HC), carbon monoxide (CO), nitrogen oxides (NOx)) contained in exhaust gas. In addition, with the recent increased environmental consciousness, regulations of exhaust gas emitted from automobiles and the like have been tightened further. With these tightened regulations, improvements of these catalysts are being advanced.
As such a catalyst for purification of exhaust gas, Japanese Unexamined Patent Application Publication No. 2012-240027 (Patent Document 1) discloses a catalyst for purification of exhaust gas comprising a catalyst layer, wherein multiple voids are present in the catalyst layer, a mode of a frequency distribution regarding diameter to length ratios (D/L) of the voids in cross-sections thereof is 2 or greater, the ratio of the voids in the catalyst layer is 15% by volume or higher and 30% by volume or lower, and a thickness of the catalyst layer at a thickest portion is 150 μm or less. However, the catalyst for purification of exhaust gas disclosed in Patent Document 1 is not necessarily sufficient in terms of a catalytic performance in a high-load region with a high gas flow rate.
Moreover, catalysts for purification of exhaust gas have been recently required to have more advanced properties, and there arises a demand for a catalyst for purification of exhaust gas capable of exhibiting an excellent catalyst performance also in a high-load region with a high gas flow rate.